Active infrared sensor

ABSTRACT

Optical transmitter  2  is equipped with transmitted pulse modulator  23.  at which a plurality of optical transmission patterns have previously been stored. The respective stored optical transmission patterns have mutually different ratios between infrared pulse ON times and OFF times. Optical output of infrared signal(s) transmitted from optical transmitter  2  is made variable as a result of the fact that infrared pulse(s) output during infrared output period(s) is or are output in accordance with an optical transmission pattern selected from among the plurality of optical transmission patterns.

BACKGROUND OF INVENTION

[0001] The present invention relates to an active infrared sensor suchas may be used in security systems and the like. In particular, thepresent invention pertains to an improvement for making variable thetransmitted optical output from an optical transmitter means.

[0002] As disclosed for example at Japanese Patent ApplicationPublication Kokai No. H13-188970 (2001), applications in which activeinfrared sensors are used in security systems to detect entry of personsinto protected areas are conventionally known. Such sensors aretypically equipped with optical transmitters employing internal opticaltransmitter elements and optical receivers employing internal opticalreceiver elements. Such optical transmitter(s) and optical receiver(s)might be arranged in opposing fashion so as to straddle a protected areasuch that infrared beam(s) from optical transmitter(s) is or aretransmitted toward optical receiver(s). Moreover, when infrared beam(s)being transmitted from optical transmitter(s) to optical receiver(s) isor are interrupted by intruder(s), causing a change in the amount oflight received by optical receiver element(s), a security camera mightfor example be activates or a security company might be contacted.

[0003] However, changes in environment and/or conditions under whichthey are used may cause optical receiver elements of such infraredsensors to become saturated, preventing satisfactory detection. Specificdescription follows. Various types of such infrared sensors areavailable, corresponding to the different sizes of protected areas inwhich they are intended to be used. For example, there are sensors foruse with distances of on the order of 100 m between optical transmitterand optical receiver, there are sensors for use with distances of on theorder of 20 m therebetween, and so forth. Transmitted optical outputfrom the optical transmitter is set in advance so as to be higher in thecase of the former as compared with the latter.

[0004] Moreover, when the former—i.e., infrared sensors intended forseparations of 100 m—are used in applications involving comparativelynarrow protected areas, e.g., where distance between optical transmitterand optical receiver is on the order of 20 m, the intensity of theso-called feedback beam produced when infrared light reflected byobjects (e.g., wall surfaces or ground surfaces) in the vicinity of thesensor other than the objects being detected irradiates the opticalreceiver can become comparatively large. As a result, despite the factthat an intruder or the like may have passed between an opticaltransmitter and an optical receiver, interrupting the infrared beamtherebetween, because this feedback beam irradiates the optical receiverthe optical receiver is unable to detect interruption of the infraredbeam by the intruder or the like, resulting in an undetected intrusionevent. Particularly where water has collected on the ground as a resultof rainfall or snow has accumulated as a result of snowfall, there is atendency for the intensity of this feedback beam to become large,increasing the likelihood of occurrence of an undetected intrusionevent. Furthermore, during times of such rainfall or snowfall, it ispossible that the intensity of the feedback beam will increase and thatan undetected intrusion event will occur even where the infrared sensoremployed is of a type designed for the size of the protected area inquestion (e.g., where optical transmitter(s) and optical receiver(s) ofinfrared sensors intended for separations of 20 m are installed suchthat they are separated by on the order of 20 m).

[0005] In order to remedy such shortcomings, it has been proposed, forexample as disclosed at Japanese Patent Application Publication KokaiNo. H5-174260 (1993), that transmitted optical output from opticaltransmitter(s) be made variable. That is, a constitution is adoptedwherein the optical transmitting circuit is equipped with a currentlimiting circuit, and the resistance of a variable resistor provided atthis current limiting circuit is varied as necessary so as to permitadjustment of transmitted optical output. For example, in the event ofthe aforementioned circumstances tending to cause intensity of thefeedback beam to become large, resistance at the variable resistor mightbe increased so as to reduce transmitted optical output. This allows theintensity of the feedback beam to be held to a low value, permittingaccurate detection of interruption of the infrared beam as a result ofpassage therethrough by the foregoing intruder or the like.

[0006] However, because the means for making transmitted optical outputvariable which is disclosed in the foregoing publication requirescomplicated electrical circuitry, in practice it is only actuallypossible to switch between on the order of two levels of transmittedoptical output.

[0007] And with a device such as this, which only permits switchingbetween on the order of two levels, depending on environment and/or theconditions under which the infrared sensor is used it may not bepossible to completely eliminate the aforementioned shortcomings causedby the feedback beam.

[0008] While a constitution that would permit switching among multiplelevels of transmitted optical output has therefore been desired, apractical solution has been difficult because of the concomitantincreased complexity in electrical circuitry which would resulttherefrom as described above.

[0009] The present invention was conceived in light of such issues, itsobject being to make it possible for the transmitted optical output inan active infrared sensor to be made variable without the need forcomplicated electrical circuitry, and to make it possible to carry outmultilevel adjustment of transmitted optical output as a result thereof.

SUMMARY OF INVENTION

[0010] In order to achieve the foregoing object, one or more embodimentsof the present invention may be such that transmitted optical output asdetermined by value(s) of integrated optical energy transmitted duringinfrared output period(s) is capable of being changed as a result ofadjustment of ratio(s) between infrared pulse ON time(s) and OFF time(s)during such infrared output period(s). That is, optical output oftransmitted infrared signal(s) may be made variable while outputvalue(s) of the respective infrared pulse(s) is or are themselves heldconstant.

[0011] More specifically, one or more embodiments of the presentinvention is or are predicated upon an active infrared sensor equippedwith one or more optical transmitter means for transmitting one or moreinfrared signals toward one or more protected areas, entry of one ormore objects into at least one of the protected area or areas beingdetected when at least one of the infrared signal or signals transmittedfrom at least one of the optical transmitter means is interrupted. Insuch an active infrared sensor, at least one of the infrared signal orsignals transmitted from at least one of the optical transmitter meansmay be produced by repeated alternation between one or more infraredoutput periods and one or more infrared non-output periods, a pluralityof infrared pulses being output during at least one of the infraredoutput period or periods. Moreover, one or more transmitted pulsemodulation means may be provided, optical output of at least one of theinfrared signal or signals transmitted from at least one of the opticaltransmitter means being made variable as a result of adjustment of atleast one ratio between infrared pulse ON time and OFF time during atleast one of the infrared output period or periods.

[0012] As a result of such specific features, by choosing large ratio(s)of infrared pulse OFF time(s) relative to ON time(s), it is possible toattain small value(s) of integrated optical energy transmitted duringinfrared output period(s) and low optical output in infrared signal(s)transmitted from optical transmitter means. Conversely, by choosingsmall ratio(s) of infrared pulse OFF time(s) relative to ON time(s), itis possible to attain large value(s) of integrated optical energytransmitted during infrared output period(s) and high optical output ininfrared signal(s) transmitted from optical transmitter means. That is,this makes it possible for transmitted optical output to be madevariable through adjustment of ratio(s) between infrared pulse ONtime(s) and OFF time(s)—which is something that can be implementedthrough software control alone; and makes it possible to carry outmultilevel adjustment of transmitted optical output without the need forcomplicated electrical circuitry—which is something that would involvehardware design.

[0013] The following may be presented as examples of specific techniquesfor making variable the optical output of infrared signal(s) transmittedfrom optical transmitter means.

[0014] In one such technique, the optical output of at least one of theinfrared signal or signals transmitted from at least one of the opticaltransmitter means is made variable by varying the number of the infraredpulses during at least one of the infrared output period or periodswhile the duration or durations of this or these infrared output periodor periods is or are held constant.

[0015] In another such technique, the optical output of at least one ofthe infrared signal or signals transmitted from at least one of theoptical transmitter means is made variable by varying the width of atleast one of the infrared pulses during at least one of the infraredoutput period or periods while the duration or durations of this orthese infrared output period or periods is or are held constant.

[0016] In yet another such technique, the optical output of at least oneof the infrared signal or signals transmitted from at least one of theoptical transmitter means is made variable by varying the duration of atleast one of the infrared output period or periods.

[0017] Use of these techniques either individually or in mutualcombination makes it possible to switch among multiple levels oftransmitted optical output.

[0018] The following may be presented as examples of specific techniquesfor adjusting ratio(s) between infrared pulse ON time(s) and OFF time(s)during such infrared output period(s).

[0019] In one such technique, a plurality of optical transmissionpatterns having mutually different ratios between infrared pulse ONtimes and OFF times are previously stored at at least one of thetransmitted pulse modulation means, optical output of at least one ofthe infrared signal or signals transmitted from at least one of theoptical transmitter means being made variable as a result of the factthat at least one of the infrared pulses output during at least one ofthe infrared output period or periods is output in accordance with anoptical transmission pattern selected from among the plurality ofoptical transmission patterns.

[0020] In another such technique, at least one of the transmitted pulsemodulation means is equipped with at least one first sending circuitcapable of determining at least one frequency of at least one set ofinfrared pulses to be output during at least one of the infrared outputperiod or periods, and at least one second sending circuit capable ofdetermining one or more durations of one or more ON times of one or moreinfrared pulses output during at least one of the infrared output periodor periods. Furthermore, at least one control signal from each of thesesending circuits may be ANDed together, and optical output of at leastone of the infrared signal or signals transmitted from at least one ofthe optical transmitter means may be made variable as a result of outputof at least one set of infrared pulses at this frequency and having thisor these ON time duration or durations during at least one of theinfrared output period or periods.

[0021] Such techniques make it possible to cause infrared pulses outputduring infrared output period(s) to be output in accordance withselected or generated optical transmission pattern(s), as a result ofwhich optical output of infrared signal(s) transmitted from opticaltransmitter means is made variable. In particular, where infrared pulsesare output at frequency or frequencies and with ON time duration(s) asdetermined by the respective aforementioned sending circuits, there isno need to prepare and store a plurality of optical transmissionpatterns in advance, permitting reductions to be achieved in requiredstorage capacity and making it possible to inhibit increases in infraredsensor cost.

[0022] Furthermore, if at least one of the optical transmitter meansand/or at least one of the optical receiver means is or are providedwith at least one activation means for activating at least onefunctionality by means of which at least one of the transmitted pulsemodulation means varies transmitted optical output, it will be possibleto cause varying of optical output of transmitted infrared signal(s) tobe carried out automatically. What this means is that there will nolonger be a need for a user to perform operations for varyingtransmitted optical output in correspondence to environment and/or theconditions under which the infrared sensor is used.

[0023] Furthermore, it will also be possible to cause varying of opticaloutput of transmitted infrared signal(s) to be carried out automaticallyif at least one of the optical receiver means is provided with at leastone request sending means capable of sending to at least one of theoptical transmitter means at least one request signal for requestingaction of at least one functionality by means of which at least one ofthe transmitted pulse modulation means varies transmitted opticaloutput.

BRIEF DESCRIPTION OF DRAWINGS

[0024]FIG. 1 is a block diagram showing the constitution of an activeinfrared sensor associated with a first embodiment.

[0025]FIG. 2(a) is a drawing showing a first optical transmissionpattern which is stored at a transmitted pulse modulator, and FIG. 2(b)is a drawing showing a transmitted optical output waveform correspondingthereto.

[0026]FIG. 3(a) is a drawing showing a second optical transmissionpattern which is stored at a transmitted pulse modulator, and FIG. 3(b)is a drawing showing a transmitted optical output waveform correspondingthereto.

[0027]FIG. 4(a) is a drawing showing a third optical transmissionpattern which is stored at a transmitted pulse modulator, and FIG. 4(b)is a drawing showing a transmitted optical output waveform correspondingthereto.

[0028]FIG. 5(a) is a drawing showing a fourth optical transmissionpattern which is stored at a transmitted pulse modulator, and FIG. 5(b)is a drawing showing a transmitted optical output waveform correspondingthereto.

[0029]FIG. 6(a) is a drawing showing a fifth optical transmissionpattern which is stored at a transmitted pulse modulator, and FIG. 6(b)is a drawing showing a transmitted optical output waveform correspondingthereto.

[0030]FIG. 7(a) is a drawing showing a sixth optical transmissionpattern which is stored at a transmitted pulse modulator, and FIG. 7(b)is a drawing showing a transmitted optical output waveform correspondingthereto.

[0031]FIG. 8(a) is a drawing showing a seventh optical transmissionpattern which is stored at a transmitted pulse modulator, and FIG. 8(b)is a drawing showing a transmitted optical output waveform correspondingthereto.

[0032]FIG. 9 is a block diagram showing the constitution of an activeinfrared sensor associated with a second embodiment.

[0033]FIG. 10 is a block diagram showing the constitution of an activeinfrared sensor associated with a third embodiment.

[0034]FIG. 11 is a block diagram showing the constitution of an activeinfrared sensor associated with a fourth embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0035] Below, embodiments of the present invention are described withreference to the drawings. In the embodiments which follow, the presentinvention is described in terms of an example in which it is applied toa sensor for detecting entry of persons into protected areas (regionswith respect to which detection is carried out), such as may be employedin security systems or the like installed in offices, factories, or thelike for nighttime monitoring thereof.

[0036] Embodiment 1

[0037] A first embodiment of the present invention will first bedescribed. FIG. 1 is a block diagram showing the constitution of anactive infrared sensor 1 associated with the present embodiment. Such anactive infrared sensor 1 might be installed at a prescribed protectedarea, and might output an alarm to a system control panel, not shown,which activates a security camera (not shown) or contacts a securitycompany when entry of a person into such protected area is detected.

[0038] As shown in FIG. 1, this active infrared sensor 1 is such thatoptical transmitter(s) 2 serving as optical transmitter means andoptical receiver(s) 3 serving as optical receiver means are arranged inprotected area(s) in opposing fashion with prescribed distance(s)therebetween along an optical axis or axes traveled by infrared pulsestransmitted by optical transmitter(s) 2 and described below.

[0039] Such an optical transmitter 2 is equipped with opticaltransmitter element(s) 21 and optical transmitter drive circuit(s) 22for driving such optical transmitter element(s) 21. Such an opticaltransmitter element 21 transmits infrared pulses (pulsed light) in theform of near-infrared beam(s). The timing with which such infraredpulses are transmitted is determined by optical transmitter drivecircuit 22. More specifically, transmission of infrared pulses may occuras a result of repeated alternation between infrared output period(s)and infrared non-output period(s), a plurality of infrared pulses beingoutput during the infrared output period(s). More detailed descriptionis given below regarding the timing with which such plurality ofinfrared pulses may be output during infrared output period(s).

[0040] Turning now to the optical receiver(s) 3, such an opticalreceiver 3 is equipped with optical receiver element(s) 31 and alarmoutput unit(s) 32. Such an alarm output unit 32 senses whether infraredpulses have been received at optical receiver element 31, and, in theevent that either a condition wherein such infrared pulses are notreceived or a condition wherein the amount of light represented byreceived infrared pulses is reduced persists for a prescribed period oftime, determines that the change in the amount of light received atoptical receiver element 31 is due to interruption of the near-infraredbeam by an intruder, in which case it outputs an alarm to a systemcontrol panel, not shown, for the purpose of activating a securitycamera or contacting a security company.

[0041] Furthermore, the distinctive feature of the present embodimentlies in the fact that transmitted pulse modulator(s) 23 serving astransmitted pulse modulation means is or are provided at the foregoingoptical transmitter(s) 2. Such a transmitted pulse modulator 23 isdescribed below.

[0042] Such a transmitted pulse modulator 23 outputs, to opticaltransmitter drive circuit 22, control signal(s) for adjusting ratio(s)between infrared pulse ON time(s) and OFF time(s) during the foregoinginfrared output period(s), as a result of which optical output ofinfrared signal(s) transmitted from optical transmitter element(s) 21 ismade variable. More specifically, stored in advance at such transmittedpulse modulator 23 are a plurality of infrared pulse opticaltransmission patterns. Moreover, one of the optical transmissionpatterns is selected in correspondence to environmental conditionsand/or the conditions under which infrared sensor 1 is used, and thisoptical transmission pattern is used to transmit a near-infrared beamtoward optical receiver 3.

[0043] At (a) in FIGS. 2 through 8, examples of optical transmissionpatterns which may be stored at such a transmitted pulse modulator 23are shown. Furthermore, at (b) in FIGS. 2 through 8, waveforms of pulsesreceived at optical receiver 3 when near-infrared beams pursuant to theforegoing respective optical transmission patterns are transmittedtoward optical receiver 3 are shown. Moreover, at (b) in FIGS. 2 through8, the dashed line indicates actual pulse waveform as received inaccompaniment to infrared pulse output, and the solid line indicatesaverage received pulse waveform as derived therefrom. The height of thereceived pulse waveform shown herein is determined by the optical outputof the infrared signal transmitted from optical transmitter element 21.Moreover, the infrared signals which may be transmitted from opticaltransmitter element 21 differ mutually with respect to optical output incorrespondence to which of the respective optical transmission patternsis employed.

[0044] The specific optical transmission patterns indicated by way ofexample in the drawings are described below. FIG. 2 shows an example inwhich the ratio between infrared pulse ON time and OFF time during aprescribed infrared output period is chosen to be 1: 3, and in which thenumber of infrared pulses during this infrared output period is chosento be 4. More specifically, infrared output period A1 is chosen to be130 μs, infrared non-output period B1 is chosen to be 500 μs, infraredpulse ON time T1 is chosen to be 10 μs, and infrared pulse OFF time T2is chosen to be 30 μs. Optical output of the transmitted infrared signalis in the present case V1.

[0045]FIG. 3 shows an example in which the ratio between infrared pulseON time and OFF time during a prescribed infrared output period ischosen to be 1: 5, and in which the number of infrared pulses duringthis infrared output period is chosen to be 3 (there being 1 less pulsethan was the case in the situation shown in FIG. 2). More specifically,infrared output period A1 is chosen to be 130 μs, infrared non-outputperiod B1 is chosen to be 500 μs, infrared pulse ON time T1 is chosen tobe 10 μs, and infrared pulse OFF time T3 is chosen to be 50 μs. Opticaloutput of the transmitted infrared signal is in the present case V2,which is lower than was the case in the situation shown in theaforementioned FIG. 2.

[0046]FIG. 4 shows an example in which the ratio between infrared pulseON time and OFF time during a prescribed infrared output period ischosen to be 1: 2, and in which the number of infrared pulses duringthis infrared output period is chosen to be 5 (there being 1 more pulsethan was the case in the situation shown in FIG. 2). More specifically,infrared output period A1 is chosen to be 130 μs, infrared non-outputperiod B1 is chosen to be 500 μs, infrared pulse ON time T1 is chosen tobe 10 μs, and infrared pulse OFF time T4 is chosen to be 20 μs. Opticaloutput of the transmitted infrared signal is in the present case V3,which is higher than was the case in the situation shown in theaforementioned FIG. 2.

[0047]FIG. 5 shows an example in which the ratio between infrared pulseON time and OFF time during a prescribed infrared output period ischosen to be 5: 2, and in which the number of infrared pulses duringthis infrared output period is chosen to be 4 (there being the samenumber of pulses as was the case in the situation shown in FIG. 2). Morespecifically, infrared output period A1 is chosen to be 130 μs, infrarednon-output period B1 is chosen to be 500 μs, infrared pulse ON time T5is chosen to be 25 μs, and infrared pulse OFF time T6 is chosen to be 10μs. Optical output of the transmitted infrared signal is in the presentcase V4, which is higher than was the case in the situation shown in theaforementioned FIG. 2.

[0048]FIG. 6 shows an example in which the ratio between infrared pulseON time and OFF time during a prescribed infrared output period ischosen to be approximately 1: 7, and in which the number of infraredpulses during this infrared output period is chosen to be 4 (there beingthe same number of pulses as was the case in the situation shown in FIG.2). More specifically, infrared output period A1 is chosen to be 130 μs,infrared non-output period B1 is chosen to be 500 μs, infrared pulse ONtime T7 is chosen to be 5 μs, and infrared pulse OFF time T8 is chosento be approximately 37 μs. Optical output of the transmitted infraredsignal is in the present case V5, which is lower than was the case inthe situation shown in FIG. 2.

[0049]FIG. 7 shows an example in which the ratio between infrared pulseON time and OFF time during a prescribed infrared output period ischosen to be 2: 1, and in which the number of infrared pulses duringthis infrared output period is chosen to be 4 (there being the samenumber of pulses as was the case in the situation shown in FIG. 2). Morespecifically, infrared output period A2 is chosen to be 55 μs, infrarednon-output period B2 is chosen to be 500 μs, infrared pulse ON time T9is chosen to be 10 μs, and infrared pulse OFF time T10 is chosen to beapproximately 5 μs. Optical output of the transmitted infrared signal isin the present case V6, which is higher than was the case in thesituation shown in the aforementioned FIG. 2.

[0050]FIG. 8 shows an example in which the ratio between infrared pulseON time and OFF time during a prescribed infrared output period ischosen to be 1: 4, and in which the number of infrared pulses duringthis infrared output period is chosen to be 4 (there being the samenumber of pulses as was the case in the situation shown in FIG. 2). Morespecifically, infrared output period A3 is chosen to be 160 μs, infrarednon-output period B3 is chosen to be 500 μs, infrared pulse ON time T11is chosen to be 10 μs, and infrared pulse OFF time T12 is chosen to beapproximately 40 μs. Optical output of the transmitted infrared signalis in the present case V6, which is lower than was the case in thesituation shown in the aforementioned FIG. 2.

[0051] Infrared pulse optical transmission patterns such as theforegoing are stored in advance at transmitted pulse modulator 23.Moreover, one of the optical transmission patterns is selected incorrespondence to environmental conditions and/or the conditions underwhich infrared sensor 1 is used, and this optical transmission patternis used to transmit a near-infrared beam toward optical receiver 3.

[0052] For example, during times of rainfall or snowfall, underconditions where the amount of light in the aforementioned feedback beamis likely to increase, an optical transmission pattern in which theoptical output of the transmitted infrared signal is set to a low value(as is the case, for example, with the optical transmission patternsshown in FIGS. 3, 6, and 8) might be selected and this opticaltransmission pattern might be used to transmit a near-infrared beamtoward optical receiver 3. Furthermore, where the distance betweenoptical transmitter 2 and optical receiver 3 is set so as to be acomparatively small value (e.g., on the order of 10 m), an opticaltransmission pattern in which the optical output of the transmittedinfrared signal is set to a low value might likewise be selected.Conversely, where the distance between optical transmitter 2 and opticalreceiver 3 is set so as to be a comparatively large value (e.g., on theorder of 100 m), an optical transmission pattern in which the opticaloutput of the transmitted infrared signal is set to a high value (as isthe case, for example, with the optical transmission patterns shown inFIGS. 4, 5, and 7) might be selected.

[0053] Such selection of optical transmission pattern(s) may be carriedout manually through user intervention or may be carried outautomatically in correspondence to environmental conditions and/or theconditions under which infrared sensor 1 is used. For example, as anexample of automatic selection, distance between optical transmitter andoptical receiver may be entered in the form of data or might be detectedautomatically, permitting optical transmission pattern(s) to beautomatically selected and control signal(s) to be output fromtransmitted pulse modulator 23 to optical transmitter drive circuit 22in correspondence thereto.

[0054] As described above, in the present embodiment, one of a pluralityof infrared pulse optical transmission patterns previously stored attransmitted pulse modulator 23 is selected in correspondence toenvironmental conditions and/or the conditions under which infraredsensor 1 is used, and this selected optical transmission pattern is usedto transmit a near-infrared beam toward optical receiver 3. Thistherefore makes it possible for transmitted optical output to be madevariable without the need for complicated electrical circuitry, andmakes it possible to carry out multilevel adjustment of transmittedoptical output as a result thereof. As a result, it is possible tocompletely eliminate the aforementioned shortcomings caused by thefeedback beam, which varies depending on environment and/or theconditions under which infrared sensor 1 is used.

[0055] Embodiment 2

[0056] A second embodiment of the present invention will now bedescribed. In the infrared sensor of the foregoing first embodiment, therespective optical transmission patterns were stored in advance attransmitted pulse modulator 23. In the present embodiment, desiredoptical transmission pattern(s) is or are generated at transmitted pulsemodulator 23. As the constitution of the present embodiment is in otherrespects similar to that of the first embodiment, description here willbe confined to that structure which is responsible for generation of theoptical transmission pattern(s).

[0057] As shown in FIG. 9, transmitted pulse modulator 23 of the presentembodiment is equipped with first and second sending circuits 23A, 23B.First sending circuit 23A is a circuit for determining frequency orfrequencies of infrared pulses output during infrared output period(s).Second sending circuit 23B is a circuit for determining duration(s) ofON time(s)—i.e., pulsewidth(s)—of infrared pulse(s) output duringinfrared output period(s).

[0058] Moreover, by ANDing together infrared pulse frequency orfrequencies and pulsewidth(s) as determined by these respective sendingcircuits 23A, 23B and outputting the result thereof to opticaltransmitter drive circuit 22, it is possible to generate desired opticaltransmission pattern(s).

[0059] For example, if the optical transmission pattern shown in FIG.2(a) is modified by applying thereto an infrared pulse frequency asdetermined by first sending circuit 23A which is set so as to be a lowvalue, the result might be an optical transmission pattern as shown inFIG. 3(a); or conversely, if infrared pulse frequency is set so as to bea high value, the result might be an optical transmission pattern asshown in FIG. 4(a).

[0060] On the other hand, if the optical transmission pattern shown inFIG. 2(a) is modified by applying thereto an infrared pulse ON timeduration as determined by second sending circuit 23B which is set so asto be a high value, the result might be an optical transmission patternas shown in FIG. 5(a); or conversely, if infrared pulse ON time durationis set so as to be a low value, the result might be an opticaltransmission pattern as shown in FIG. 6(a).

[0061] In the present embodiment, by combining infrared pulse frequencyor frequencies and pulsewidth(s) as determined by these respectivesending circuits 23A, 23B, it is thus possible to generate opticaltransmission pattern(s) of arbitrary profile. The present embodimenttherefore allows optical output of transmitted infrared signal(s) to beswitched among multiple levels by means of a transmitted pulse modulator23 which need not have large storage capacity as compared with that ofthe first embodiment,.

[0062] Embodiment 3

[0063] A third embodiment of the present invention will now bedescribed. The present embodiment relates to a constitution for causingoptical output of transmitted infrared signal(s) to be variedautomatically. As the constitution of the present embodiment is in otherrespects similar to that of the foregoing first embodiment, descriptionhere will be confined to that structure which is responsible for causingtransmitted optical output to be varied automatically.

[0064] As shown in FIG. 10, optical transmitter 2 of the presentembodiment is provided with activation circuit(s) 24 serving asactivation means for activating the ability of transmitted pulsemodulator(s) 23 to vary transmitted optical output. Optical transmissionpattern(s) selected as described above is or are again selected throughaction of this activation circuit 24 in correspondence to environmentalconditions and/or the conditions under which infrared sensor 1 is used,and such selected optical transmission pattern(s) is or are used totransmit a near-infrared beam toward optical receiver 3.

[0065] The timing with which such an activation circuit 24 operates maybe such that it operates at one or more prescribed preset times and/oras may be determined in correspondence to change(s) in ambienttemperature, change(s) in ambient illumination, or the like.

[0066] This makes it possible for varying of optical output oftransmitted infrared signal(s) to be carried out automatically,eliminating the need for a user to perform operations for varyingtransmitted optical output in correspondence to changes in environmentand/or conditions under which the infrared sensor is used.

[0067] Furthermore, such an activation circuit 24 may be provided atoptical receiver 3 instead of optical transmitter 2. Furthermore,activation circuits 24 may be provided at both optical transmitter 2 andoptical receiver 3.

[0068] Furthermore, activation circuit(s) 24 in accordance with thepresent embodiment may be provided at at least one optical transmitter 2and/or at least one optical receiver 3 of the foregoing secondembodiment.

[0069] Embodiment 4

[0070] A fourth embodiment of the present invention will now bedescribed. The present embodiment also relates to a constitution forcausing optical output of transmitted infrared signal(s) to be variedautomatically. As the constitution of the present embodiment is in otherrespects similar to that of the foregoing first embodiment, descriptionhere will be confined to that structure which is responsible for causingtransmitted optical output to be varied automatically.

[0071] As shown in FIG. 11, optical receiver 3 of the present embodimentis provided with request sending circuit 33 serving as request sendingmeans capable of sending, to optical transmitter 2, request signal(s)for requesting action of functionality by means of which transmittedpulse modulator(s) 23 varies or vary transmitted optical output.Selected optical transmission pattern(s) is or are selected throughaction of this request sending circuit 33 in correspondence toenvironmental conditions and/or the conditions under which infraredsensor 1 is used, and such selected optical transmission pattern(s) isor are used to transmit a near-infrared beam toward optical receiver 3.

[0072] The timing with which such a request sending circuit 33 operatesmay be such that it operates as determined in correspondence to presetprescribed time(s) and/or the like.

[0073] The present embodiment also makes it possible for varying ofoptical output of transmitted infrared signal(s) to be carried outautomatically, eliminating the need for a user to perform operations forvarying transmitted optical output in correspondence to environmentand/or conditions under which the infrared sensor is used.

[0074] In addition, in the present embodiment, request signal(s) may besent from request sending circuit 33 to optical transmitter 2 either inwireless fashion and/or via wiring.

[0075] Furthermore, request sending circuit(s) 33 in accordance with thepresent embodiment may be provided at optical receiver(s) 3 of theforegoing second embodiment.

[0076] Other Embodiments

[0077] Whereas in the several foregoing embodiments the presentinvention has been described in terms of an example in which it isapplied to a sensor such as may be used in a security system, thepresent invention is not limited thereto but may also be applied to awide variety of applications, such as use in sensors for activating ATMs(machines that automatically accept deposit of and/or dispense cash)installed at banks or the like, and so forth.

[0078] Furthermore, the active infrared sensor associated with thepresent invention is not limited to applications in which the object(s)being detected is or are person(s).

[0079] Moreover, the present application claims right of benefit ofprior filing date of Japanese Patent Application No. 2002-23104, thecontent of which is incorporated herein by reference in its entiretyFurthermore, all references cited in the present specification arespecifically incorporated herein by reference in their entirety.

What is claimed is:
 1. In the context of an active infrared sensorequipped with one or more optical transmitter means for transmitting oneor more infrared signals toward one or more protected areas, entry ofone or more objects into at least one of the protected area or areasbeing detected when at least one of the infrared signal or signalstransmitted from at least one of the optical transmitter means isinterrupted, an active infrared sensor characterized in that: at leastone of the infrared signal or signals transmitted from at least one ofthe optical transmitter means is produced by repeated alternationbetween one or more infrared output periods and one or more infrarednon-output periods, a plurality of infrared pulses being output duringat least one of the infrared output period or periods; and it isequipped with one or more transmitted pulse modulation means capable ofcausing optical output of at least one of the infrared signal or signalstransmitted from at least one of the optical transmitter means to bemade variable as a result of adjustment of at least one ratio betweeninfrared pulse ON time and OFF time during at least one of the infraredoutput period or periods.
 2. An active infrared sensor according toclaim 1 characterized in that it is constituted such that at least oneof the transmitted pulse modulation means makes variable the opticaloutput of at least one of the infrared signal or signals transmittedfrom at least one of the optical transmitter means by varying the numberof the infrared pulses during at least one of the infrared output periodor periods while the duration or durations of this or these infraredoutput period or periods is or are held constant.
 3. An active infraredsensor according to claim 1 or 2 characterized in that it is constitutedsuch that at least one of the transmitted pulse modulation means makesvariable the optical output of at least one of the infrared signal orsignals transmitted from at least one of the optical transmitter meansby varying the width of at least one of the infrared pulses during atleast one of the infrared output period or periods while the duration ordurations of this or these infrared output period or periods is or areheld constant.
 4. An active infrared sensor according to claim 1, 2, or3 characterized in that it is constituted such that at least one of thetransmitted pulse modulation means makes variable the optical output ofat least one of the infrared signal or signals transmitted from at leastone of the optical transmitter means by varying the duration of at leastone of the infrared output period or periods.
 5. An active infraredsensor according to any one of claims 1 through 4 characterized in thatit is constituted such that a plurality of optical transmission patternshaving mutually different ratios between infrared pulse ON times and OFFtimes are previously stored at at least one of the transmitted pulsemodulation means, optical output of at least one of the infrared signalor signals transmitted from at least one of the optical transmittermeans being made variable as a result of the fact that at least one ofthe infrared pulses output during at least one of the infrared outputperiod or periods is output in accordance with an optical transmissionpattern selected from among the plurality of optical transmissionpatterns.
 6. An active infrared sensor according to any one of claims 1through 4 characterized in that it is constituted such that at least oneof the transmitted pulse modulation means is equipped with at least onefirst sending circuit capable of determining at least one frequency ofat least one set of infrared pulses to be output during at least one ofthe infrared output period or periods, and at least one second sendingcircuit capable of determining one or more durations of one or more ONtimes of one or more infrared pulses output during at least one of theinfrared output period or periods, at least one control signal from eachof these sending circuits being ANDed together, and optical output of atleast one of the infrared signal or signals transmitted from at leastone of the optical transmitter means being made variable as a result ofoutput of at least one set of infrared pulses at this frequency andhaving this or these ON time duration or durations during at least oneof the infrared output period or periods.
 7. An active infrared sensoraccording to claim 5 characterized in that it is such that at least oneof the infrared signal or signals transmitted from at least one of theoptical transmitter means is capable of being received by one or moreoptical receiver means arranged on one or more optical axes thereof; atleast one of the optical transmitter means and/or at least one of theoptical receiver means being provided with at least one activation meansfor activating at least one transmitted optical output varyingcapability of at least one of the transmitted pulse modulation means. 8.An active infrared sensor according to claim 6 characterized in that itis such that at least one of the infrared signal or signals transmittedfrom at least one of the optical transmitter means is capable of beingreceived by one or more optical receiver means arranged on one or moreoptical axes thereof; at least one of the optical transmitter meansand/or at least one of the optical receiver means being provided with atleast one activation means for activating at least one transmittedoptical output varying capability of at least one of the transmittedpulse modulation means.
 9. An active infrared sensor according to claim5 characterized in that it is such that at least one of the infraredsignal or signals transmitted from at least one of the opticaltransmitter means is capable of being received by one or more opticalreceiver means arranged on one or more optical axes thereof; at leastone of the optical receiver means being provided with at least onerequest sending means capable of sending to at least one of the opticaltransmitter means at least one request signal for requesting action ofat least one functionality by means of which at least one of thetransmitted pulse modulation means varies transmitted optical output.10. An active infrared sensor according to claim 6 characterized in thatit is such that at least one of the infrared signal or signalstransmitted from at least one of the optical transmitter means iscapable of being received by one or more optical receiver means arrangedon one or more optical axes thereof; at least one of the opticalreceiver means being provided with at least one request sending meanscapable of sending to at least one of the optical transmitter means atleast one request signal for requesting action of at least onefunctionality by means of which at least one of the transmitted pulsemodulation means varies transmitted optical output.